The M-16 automatic rifle has been a standard weapon of choice for the U.S. Military. The M-16 family of weapons includes semi-automatic counterparts which are popular with the civilian sector. The structure and mechanisms of these weapons, and improvements and variations thereto, have been the subject of many patents over the years. U.S. Pat. Nos. 2,951,424 and 3,198,076 to Stoner provide early examples of the M-16 type of weapon. In recent years, many variations and modifications of the M-16 family have evolved.
Generally, the M-16 family of automatic and semi-automatic rifles is based on a gas-operated bolt carrier system. The bolt carrier system includes a multi-lug bolt that interlocks, within the receiver, with a barrel extension engaged to the rifle barrel for firing each round of ammunition. The bolt also includes a spring-loaded extractor configured to releasably engage a cartridge as it is placed in the firing chamber. When the rifle is fired, the interlocked bolt receives the recoil force that is transmitted from the face of the bolt to its lugs. The lugs in turn transmit the recoil force to corresponding lugs of the barrel extension. Once the round is fired, the bolt unlocks from the barrel extension and the bolt carrier recoils. As it recoils, the extractor pulls the expended cartridge from the firing chamber. The cartridge is then ejected, as is well known in the art, to allow chambering of another round by the bolt assembly. This process may then be repeated as often as desired by the shooter until the last cartridge is expended.
As used herein, “gun” or “firearm” refers to a completely assembled weapon including not only a receiver operable to fire rounds of ammunition, but also any other structure normally associated with the given weapon. Also as used herein, a “receiver” includes a barrel extension, barrel interface, or any other part or assembly of a gun or firearm that has one or more surfaces configured to engage lugs of a breech bolt.
The design of the bolt carrier and bolts used in such weapons has been the subject of previous patents. For example, U.S. Pat. No. 5,351,598 to Schuetz discloses a new type of bolt for an automatic weapon. A portion of some of the lugs on the front face of the bolt have been removed to allow easier chambering of short, low pressure pistol cartridges in an M-16 rifle.
U.S. Pat. No. 6,182,389 to Lewis discloses a bolt with a body having a number of lugs extending therefrom, as well as an extractor pivotably engaged in a recess formed in the bolt, the extractor having a pair of flanges configured to engage a pair of springs disposed on either side of a firing pin bore extending through the bolt.
While the prior art has addressed some of the deficiencies in the design of bolts and bolt carriers of automatic and semi-automatic rifles, there still exists many problems in the use of such assemblies. It is well known that the bolts are subject to failure due to the extreme stresses and temperatures to which they are subjected from repeated firing of the gun. This problem is particularly focused with respect to the lugs projecting from the main body of the bolt. As described above, the lugs are used to transfer the force from the firing of the cartridge to the barrel of the rifle. This problem is exacerbated further by the fact that automatic and semi-automatic rifles typically employ an unsymmetrical locking system in order to accommodate the extractor. The lack of symmetry of the load bearing portion of the bolt results in an uneven stress distribution among the lugs. Thus, the lugs of bolts for rifles are subject to structural failure due to the repeated high stresses induced by firing the rifle.
One of the common structural failures occurs at the lugs adjacent to the recess formed in the body of the bolt to accommodate the extractor. In forming this recess , the adjacent lugs are typically undercut and weakened relative to the other lugs.
These failures limit the overall reliability of the weapon, sometimes represented as Mean-Time-Between-Failure (MTBF). By reducing the frequency of these failures, maintenance-actions for the gun are correspondingly reduced and overall reliability is improved.
Another problem known in the art involves the extractor that is typically coupled to a bolt of an automatic or semi-automatic rifle. The extractor is known to malfunction, thus causing a jamming of the rifle due to the spent cartridge remaining in the firing chamber. As previously described, the extractor is typically spring-loaded. In the prior art extractors, the spring has a relatively short length due to the small amount of space between the outer surface of the bolt and the firing pin bore defined by the bolt for receiving the firing pin. The short length of the spring makes it much more difficult to control and maintain the tension to ensure it remains at the proper setting.
While the prior art devices attempt to address some of the problems with bolts and bolt carriers for rifles, there are still problems existing in the art requiring a need for a bolt that effectively addresses those problems. The present invention is directed toward providing various improvements to bolt carriers and bolts for automatic and semi-automatic rifles, and addresses the problems and the shortcomings of the prior art in a novel and unobvious way.